Silicon carbide (SiC) has a band gap that is about 2 to 3 times that of Si, which is widely used as a material for electronic devices and the like, and has a dielectric breakdown voltage that is about 10 times higher than that of Si. Accordingly, SiC crystals hold promise as a substrate material power devices that surpass devices which silicon is used. Herein SiC substrates are obtained by being cut out of a SiC-single crystal ingot. Known methods for producing SiC ingots include methods (vapor phase growth) in which a SiC crystal is grown in a vapor phase and methods (liquid phase growth) in which a SiC crystal is grown in a liquid phase. As compared with vapor phase growth, liquid phase growth involves growing a crystal in a state close to thermal equilibrium, and hence a high-quality SiC single crystal of low defect density is expected to be obtained as a result.
Desirably, the reliability of SiC should be high, and costs low, in order for SiC to be widely adopted as a substrate material for power devices. It has been reported that enhancement of reliability upon integration into a device is significantly affected by dislocation defects in SiC single crystals. There is thus a demand for production technologies of high-quality SiC single crystals having few dislocation defects. In terms of reducing production costs, meanwhile, technical studies aimed at achieving larger crystal sizes are being conducted in order to secure the number of chips are cut out of a SiC single-crystal ingot (wafer).
Crystal growth techniques are thus required that allow both improving the quality and increasing the size of SiC single crystals, in terms of promoting the adoption of SiC power devices.
As regards improving the quality of SiC single crystals, it has been reported that when crystal growth is performed on a seed crystal substrate having an off-angle (hereafter, referred to as off-substrate) in accordance with a liquid phase growth method, threading screw dislocations and/or threading edge dislocations extending parallelly to the growth direction are converted to defects in the basal plane, and accordingly growth-derived defects are swept outside the crystal, as a result of which dislocation density in the grown crystal can be dramatically reduced (PTL 1 and NPL 1).
On the other hand, issues that arise when the size of SiC single crystals is increased include for instance the occurrence of surface roughening at the growth interface during crystal growth. Surface roughening is extremely difficult to repair once the former has occurred during crystal growth, and accordingly further crystal growth becomes virtually impossible. The phenomenon of surface roughening is particularly noticeable during crystal growth on off-substrates. Therefore, it has been proposed to add an additive component to the growth atmosphere, or to reduce the temperature gradient in the vicinity of the growth interface, or to control solvent flow, in order to prevent surface roughening (NPL 2, 3 and 4).